Add .JuliaFormatter.toml

[inkydragon]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.41379% with 3 lines in your changes missing coverage. Please review.

Project coverage is 96.91%. Comparing base (e005ee0) to head (18af124).

Files with missing lines	Patch %	Lines
src/partitions.jl	96.42%	2 Missing :warning:
src/combinations.jl	92.85%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #191      +/-   ##
==========================================
- Coverage   97.22%   96.91%   -0.31%     
==========================================
  Files           8        8              
  Lines         829      843      +14     
==========================================
+ Hits          806      817      +11     
- Misses         23       26       +3     

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[inkydragon]

TODO: add a .git-blame-ignore-revs when merged this pr.

https://github.com/JuliaLang/julia/blob/master/.git-blame-ignore-revs

[oameye]

big fan of adding a formatter. We should probably also add CI for JuliaFormatter with https://github.com/julia-actions/julia-format